Chapter 18

Fertigation Systems for Vineyards

Design Considerations for Fertigation Systems

A permanently installed injector should be plumbed off the main waterline (water bypass), which will permit clean water to flow through the irrigation line to purge the line of fertilizer solution or supply water to crops when fertilizer is not needed. A bypass installation also allows easy removal of the unit in case of malfunction or the need for maintenance.

Injection Point

The injection point should be located so that the injected fertilizer and the irrigation water can become thoroughly mixed well upstream of any branching of the flow. There are clear arguments for injecting chemicals either upstream or downstream of the filter. The primary reason for injecting upstream of the filters is that any introduced contaminants or immediate chemical precipitations resulting from chemigation will be trapped by the filters, and thereby, the irrigation system will be saved.

In-Line Injection, Continuous Method

Most vineyard operations use in-line injection (i.e., injectors) for fertigation. Injectors take a small amount of concentrated chemical solution, such as water-soluble fertilizer dissolved in water in a stock tank, and introduce it into the irrigation line as a dilute solution at the proper concentration for delivery to plants. Injectors are also used to apply pesticides, plant growth regulators, wetting agents, disinfectants, and mineral acids during crop production. In-line injection is generally more popular than dilute tank systems since they do not require large holding tanks and they offer more flexibility. With in-line systems, concentrated stock solutions are continuously injected into the water stream as irrigation events are underway.

Nutrient Stock Tanks

The concentrated mixes of nutrients for the crop are stored in the nutrient stock tanks. Flat-bottom vertical storage tanks are very common, and they are rated to handle fertilizers. Nutrients are premixed into concentrated solutions according to recipes formulated to provide vines with all their requirements for growth. These nutrients are mixed with fresh water to make the nutrient solution that supplies the vines with both water and nutrients. Fertigation systems generally have two nutrient stock tanks and one or two pH-regulating stock tanks.

Fertilizer Mixing Procedures

Proper mixing procedures should always be followed with all fertilizer formulations. Mixing procedures are listed as follows.

pH/EC Meters

Fertigation systems contain a pH meter to constantly measure the pH of the nutrient solution and adjust it to meet the requirements. The pH is important as the optimal uptake of nutrients by crops is pH-dependent. Fertigation systems contain an EC meter in the mixing tank to constantly measure the EC of the nutrient solution and adjust it to meet the requirements. The EC is a measure of the total dissolved mineral ions present in the nutrient solution.

pH/EC Meters

Fertigation systems contain a pH meter to constantly measure the pH of the nutrient solution and adjust it to meet the requirements. The pH is important as the optimal uptake of nutrients by crops is pH-dependent. Fertigation systems contain an EC meter in the mixing tank to constantly measure the EC of the nutrient solution and adjust it to meet the requirements. The EC is a measure of the total dissolved mineral ions present in the nutrient solution.

Automated Control Systems

When automated injection controls are used, it is possible to rapidly change the dilute solution concentration by adding stock materials relative to the water flow. This is useful if the feed strength needs to be adjusted throughout the day to match growing conditions or if the feed recipes or nutrient concentration need to be changed for various crops. In some instances, the actual fertilizer formulation can be changed by either switching to different sets of stock tanks or employing a single-element dosing design where the individual fertilizer constituents are separated into several stock tanks.

Backflow Prevention Devices

Backflow can occur in a system due to a cross connection between a water source and an irrigation system. For example, water may be turned off, but the chemical injection unit may continue to work, contaminating the water source. To protect groundwater from chemical contamination, backflow—whether from back-siphonage or back pressure—must be prevented. Back-siphonage is the reversal of normal system flow, caused by negative pressure (vacuum or partial vacuum) in the supplying pipe. Back-siphonage occurs when there is a low pressure in the water source. For example, the mainline source pipe may break at a spot lower than the irrigation system, or pressure may be reduced drastically because a supply pump fails. Such situations can be avoided by installing check values, vacuum relief valves, or vacuum breaker valves.

Scheduling Fertigation

Two basic schedules for applying liquid fertilizers are constant and periodic. The application of a dilute fertilizer solution each time the crop is irrigated is known as constant fertilization, and the concentration of this applied fertilizer solution is exactly the nutrient concentration desired in the growing medium solution. Periodic fertilization consists of applying a more concentrated fertilizer solution according to some fixed schedule, such as once a week or every other irrigation.

Injection Duration

A minimum injection time of 45 to 60 minutes is recommended. This time is sufficient for the uniform distribution of nutrients throughout the fertigation zone. Injection of “slugs” (highly concentrated solutions of fertilizer usually injected in much less than 45 minutes) is not recommended. They often result in nonuniform fertilizer applications and subsequent poor crop performance.

Click on the following topics for more information on fertigation systems for vineyards.